Rotary piston pump



Oct. 4, 1966 e. F. SCHIMKAT 3,276,388

' ROTARY PISTON PUMP Filed Dec. 7, 1964 5 Sheets-Sheet l Fig.1

Inven/an- WWCIW Oct. 4, 1966 G. F. SCHIMKAT 392761388 ROTARY PISTON PUMP Filed Dec. 7, 1964 5 Sheetsheet 2 Fig.3

inventor M P Z r G. F. SCHIMKAT ROTARY PISTON PUMP Oct. 4, 1966 5 Sheets-Sheet 5 Filed Dec. '7, 1964 Fig.5

Inventor:

- Z5171 /II United States Patent 0 3,276,388 ROTARY PISTON PUMP Gerhard Franz Schimlkat, Scholzplatz 7, Berlin, Charlottenburg, Germany Filed Dec. 7, 1964, filer. No. 416,564 19 Claims. (Cl. 103-126) The present invention relates to a rotary piston pump and more particularly to a rotary piston pump of the type in which the pistons of a rotor move along an annular recess to transport a fluid from an inlet to an outlet, and also project through openings in a lock rotor to turn the same about an eccentric axis while the lock rotor projects into the recess to separate the inlet from the outlet.

The rotor of a pump of this type is exposed to a substantial axial pressure since the fluid pressure in the recess acts on the flange of the rotor which carries the pistons. As a result, very heavy thrust bearings, or an abutment of the rotor on a housing face is necessary, causing great friction losses.

It is one object of the invention to overcome this disadvantage of known rotary piston pumps of this type, and to provide an arrangement by which the rotor is relieved of axial pressure.

Another object of the invention is to provide a cover plate for the recess in which the pistons move, and to counterbalance the forces acting on the front of the cover plate by fluid pressure acting on the back of the cover plate.

Another object of the invention is to provide in the housing of the pump, a cavity, and to admit pressure fluid to this cavity so that a cover plate is pressed against a stator surface to close the recess in which the pistons of the rotor produce high pressure zones.

Another object of the invention is to provide a lower fluid pressure in the cavity than in the high pressure zone of the pump.

Another object of the invention is to permit a throttled flow of pressure fluid through the cavity in order to maintain the desired pressure therein.

Another object of the present invention is to counterbalance a tilting moment produced by the fluid on the cover plate by supplying pressure fluid to the gap between the cover plate and the stator in the low pressure region of the pump.

With these objects in View, one embodiment of the invention comprises a housing having a surface formed with an annular recess communicating with a cavity and with inlet means and outlet means; a first rotor mounted in the housing for turning movement about a first axis and having pistons projecting into the annular recess to transport a fluid from the inlet means to the outlet means; a second lock rotor mounted in the annular recess for turning movement about a second axis and having openings into which some of the rotor pistons project so that the lock rotor is rotated by the pistons of the first rotor. The lock rotor is disposed to separate the inlet means from the outlet means and located in a circular recess portion which is eccentric to a circular recess portion along which the pistons of the first rotor move. The two recess portions have a common portion, and in this region, the pistons of the first rotor pass into the openings of the lock rotor.

In accordance with the invention, a plate or cover is located in the cavity and has on one side a face slidably engaging the surface of the housing in which the recess is provided, and also a face of the lock rotor so that both circular portions of the annular recess are completely covered. The cover plate has circumferentially spaced openings through which the pistons of the first rotor project toward the annular recess, and is mounted for "ice rotation about the axis of the first rotor, and preferably directly on the same.

The cover plate is also mounted for axial movement, preferably on the first rotor, so that the face of the cover plate and the surface of the housing in which the recess is provided, form a variable gap through which pressure fluid passes from the recess into the cavity on the other side of the cover plate. The pressure in the cavity is somewhat less than the pressure in the high pressure area of the recess, but is selected to be suflicient to urge the cover plate toward the recess until a condition of equilibrium is reached in which the thickness of the gap between the cover plate and the surface with a recess is substantially constant. Since in this manner all fluid pressure prevailing in the recess is taken up by the cover plate, no axial pressure is exerted on the first rotor.

In the preferred embodiment of the invention, the housing has throttling openings connecting the cavity with the outside, so that a continuous flow of fluid takes place through the gap into the cavity of the housing and from there to the outside. In this manner, a pressure lowor than the pump pressure is produced in the cavity, and such pressure can be adjusted so that the cover plate is held in the desired position in which the losses are a minimum.

In one embodiment of the invention, the first rotor has shaft portions mounted in bearings of the housing, which are so constructed that fluid can flow out of the housing between the shaft portions and the bearing faces which form in this manner a throttling passage.

In order to permit an immediate starting of the pump, it is advantageous to provide means limiting the axial movement of the cover plate in the direction away from the surface having a recess.

In the preferred embodiment of the invention, the surface having the recess is formed with a groove in the low pressure region of the inlet means, and a housing has a duct for supplying high pressure fluid to the groove, so that the one-sided tilting moment produced by the high pressure fluid in the recess is balanced by the pressure fluid in the groove, and the face of the cover plate remains parallel to the surface ofthe housing.

A corresponding groove may be provided on the high pressure side of the pump, and connected by a duct to the low pressure side to achieve counterbalancing of the cover plate under all operational conditions.

In one embodiment of the invention, the first rotor is mounted for limited axial movement in the housing, and urged in one direction by fluid pressure. Spring means are provided for holding the rotor in the desired position against the action of the fluid pressure.

It is advantageous, to hold the radial dimension of the surface on which the cover plate slides to a minimum to reduce friction losses. Therefore, the surface may be wider in the region of the counterbalancing groove.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of Specific embodiments when read in connection with the accompanying drawings, in which:

FIG. 1 is a longitudinal axial sectional view of one embodiment of a rotary piston pump according to the present invention;

FIG. 2 is a cross sectional view taken on line AB in FIG. 1;

FIG. 3 is a fragmentary elevation illustrating the surface of the housing in which the annular recess and the counterbalancing grooves are provided;

FIG. 4 is a diagrammatic view illustrating the forces acting on the cover plate during operation of the pump; and

FIG. is a section as seen in the direction of arrows from the line C-D of FIG. 2.

Referring now to the drawings, and more particularly to FIGS. 1 and 2, the hydraulic machine of the illustrated embodiment is assumed to be a pump, and will be correspondingly described. However, it will be understood that the same machine can be used as a motor.

The machine has a housing including a stator portion 4, and a bell-shaped cover 5 secured to stator 4 by suitable means, not shown, to form a cavity 15. Stator portion 4 has a planar surface 4a which is formed with an annular recess composed of two eccentrically disposed circular recess portions 6 and 6a which coincide on one side, as best seen in FIG. 3, and are separated on the other side by a crescent-shaped wall 7.

A lock rotor 8 is mounted for free turning movement in recess portion 6a.

Inlet means 20 and outlet means 18 communicate with diametrically opposite parts of the circular recess portion 6, as best seen on the right side of FIG. 2 where part of the stator is shown broken off along line 32. The portion of lock rotor 8 located in the region where the recess portions 6 and 6a coincide, that is in the upper parts of FIGS. 1, 2 and 3, separates inlet 20 from outlet 18.

Lock rotor 8 has a plurality of circumferentially spaced peripheral openings including a number of openings 19 communicating with outlet 18, and a number of openings 21 communicating with inlet 20. Openings 19 and 21 pass through the entire thickness of lock rotor 8, as best seen in the upper part of FIG. 1. Between the openings 19 and 21, the cross section of lock rotor 8 matches the cross section of recess portion 6a, as best seen in the lower part of FIG. 1 so that the lock rotor can perform the desired sealing function where recess portions 6 and 6a coincide.

Housing part 5 has a bearing face 16, and stator 4 has a coaxial bearing face 17. Shaft portions 3a and 3b of the rotor 2 are supported on bearing faces 16 and 17 for rotation about an axis which is eccentric to the axis of lock rotor 8, corresponding to the eccentric position of the recess portions 6 and 6a. The middle part of rotor 2 is a large flange from which a plurality of pistons 1 project in axial direction into recess portion 6. The cross sectional shape of pistons 1 is best seen in FIG. 2 from which it will become apparent that pistons 1 divide the part of the recess portion 6 which is located outside of the crescent-shaped wall 7 into chambers so that during rotation of rotor 2 in counterclockwise direction as viewed in FIG. 2, fluid supplied to inlet 20 will be transported to outlet 18 and discharge therefrom. In the region of outlet 18, pistons 1 pass into openings 19 in the lock rotor, abutting at first the inner surface of openings 19, and in the region of the inlet 20, pistons 1 pass out of openings 21 finally abutting the inner surfaces of openings 21 so that no fluid can be transported from outlet 18 to inlet 20, while the lock rotor is rotated in counterclockwise direction by the pistons in synchronism with the turning movement of rotor 2.

A drive shaft 12 projects into housing 5 and has a flange 30 abutting an inner face in housing portion 5a. Drive shaft 12 has an inner splined or grooved end engaging corresponding axial recesses in the interior of rotor 2, and particularly in shaft portion 3, so that drive shaft 12 rotates rotor 2. A spring 11 is located in the interior of shaft portion 3b and abuts the end face of drive shaft 12 and an inner end face of shaft portion 3]) to urge the rotor 2 to the right as viewed in FIG. 1, flange 30 limiting movement of drive shaft 12 to the left. The diameter of shaft portion 3b is greater than the diameter of shaft portion 3, and the outer end face of shaft portion 312 closes a cavity in stator 4 which communicates with the outside through an opening 29. While the entire recess portion 6a for the lock rotor 8 is provided in stator portion 4, the separate recess portion 6 outside of crescent-shaped wall 7 is not closed by a bottom provided by stator 4, but is closed by part-circular member 9 which has such a circumferential length as to extend between the inlet and the outlet, as best seen in the lower portion of FIG. 2. Member 9 has an axially disposed rack portion 9a meshing with a drive pinion 10. The parts projecting from stator 4, are enclosed in a housing part 31 which is penetrated by the shaft, not shown, of pinion 10. This shaft can be turned with pinion 10 to move member 9 in axial direction whereby rotor 2 can be displaced in axial direction against the action of spring 11. In this manner, the volume of recess portion 6, and the amount of fluid transported by pistons 1 in recess portion 6 can be adjusted. In a modified embodiment of the invention, members 9, 10 and 31 are omitted and stator 4 provided with a recess portion 6 bounded by a bottom wall provided by the stator 4. The pressure prevailing in cavity 15 urges rotor 2 to move to the right as viewed in FIG. 1 so that pistons 1 are pressed against the bottom of recess portion 6, or more particularly against the end face of the part-circular member 9. The end faces of pistons 1, which slide on the end face of member 9, are advantageously slanted so that a Wedgeshaped accumulation of oil improves the sliding friction between pistons 1 and member 9. When the pump is at a standstill, spring 11 urges rotor 2 to a position in which the end faces of pistons 1 abut the end face of member 9 so that the pump is in an operative position and can be started.

If in the above described pump, the flange of rotor 2 would abut surface 4a, the pressure in recess portion 6 would act in axial direction on rotor 2, urging the same to the left, which would necessitate a support of rotor 2 in axial direction against such movement.

This is prevented in accordance with the present invention by the provision of a cover plate 13 located between the flange of rotor 2 and surface 4a of stator 4. Cover plate 13 has openings 13a passing therethrough, so that pistons 1 can project through openings into annular recess 6, 6a. Cover plate 13 is annular and supported by a circular support means 14 for turning movement about the axis of rotor 2, and also for limited axial movement toward and away from surface 4a. The support means 14 is secured to the stator 4. A stop flange of support means 14 defines the greatest distance which face 26 of cover plate 13 can be spaced from surface 4a of stator 4. If the gap between face 26 and surface 4a would be too wide, the pump could not be started. The pressure prevailing in recess 6, 6a is transmitted to cover plate 13 which is urged to the left as viewed in FIG. 1, but such movement is counteracted by the pressure of the fluid in cavity 15. The exact position of cover plate 13 in relation to surface 4a and to recess 6, 6a is determined by the presure in cavity 15.

FIG. 5 shows that the cover plate 13 may be biased by comparatively soft helical springs 39 which are accommodated in recesses 38 provided in the rotor 2. The springs 39 urge the cover plate 13 against the surface 4a of the stator 4.

Cavity 15 is filled with the pumped fluid, for example with oil, or is filled during the first revolutions of rotor 2 with cover plate 13 and lock rotor 8 since cover plate 13 loosely abuts stator portion 4 so that the oil can pass through the wide gap 24 between cover plate 13 and surface 4a. As soon as cavity 15 is filled completely, so that a certain pressure prevails therein, the cover plate 13 is urged toward the right as viewed in FIG. 1 and face 26 thereof closely approaches surface 4a. In this manner, further flow of pressure fluid through the gap 24 between face 26 and surface 4a is reduced or interrupted, so that cover plate 13 remains in a position of equilibrium. In practical operation, some fluid leaks to the outside between the bearing face 16 and the shaft,

portion 3a into a chamber 27 and through an opening 28, and between the bearing face 17 and the shaft portion 3b and through an opening 29. The throttling action of the passages between 3a, 16 and 3b, 17 determines the amount of leakage flow and hence the pressure in the cavity which is lower than the maximum pressure prevailing in the outlet region of the recess portion 6 so that a narrow gap 24 remains between the cover plate 1.3 and stator 4 through which pressure fluid passes into the cavity 15 so that the friction between the cover plate 13 and stator 4 is extremely low. However, since the surface of cover plate 13 exposed to pressure in cavity 15 is greater than the portions of face 26 exposed to the pressure in recess portion 6, the equilibrium of the cover plate can be maintaine-d.

A uniform pressure prevails in cavity 15 and acts on cover plate 13, as indicated in the lower portion of FIG. 4 by arrows 35. The pressure on face 26 of cover plate 13 is asymmetrical as indicated by arrows 37 in the upper portion of FIG. 4. In the region of outlet 18, the openings 19 of lock rotor 8 are directly connected to outlet 18 and are consequently filled with high pressure fluid, so that a substantial pressure is exerted on the corresponding face portions of cover plate 13. In the region of inlet 20, openings 21 of lock rotor 8 are filled by fluid at lower pressure, and the intermediate openings have intermediate pressures. Consequently, a moment acts on cover plate 13 which tends to tilt cover plate 13 and subjects the cover plate to unsymmetrical forces tending to tilt the cover plate.

In accordance with the present invention, the surface 4a is provided in the region of the lower pressure near inlet 20, with a part-circular groove 22 which is connected by a duct 25 to the high pressure side of the pump. The effective surface of groove 22 is selected so that a tilting moment is exerted on cover plate 13 which is sufficient to compensate the tilting moment produced by the higher and lower pressure on opposite sides of the pump and lock rotor. The circumferential length of groove 22 must be suflicient to assure that groove 22 extends along all chambers of recess 6, 6a in which suction pressure or low pressure prevails, so that cavity 15 does not communicate with low pressure areas of the pump. When cover plate 13 is held in a position in which face 25 is parallel to surface 4a, and with pressure fluid in groove 22 separating cavity 15 from the low pressure fluid areas of the pump, no fluid flows from cavity 15 into the gap between cover plate 13 and stator 4 which is of importance for the stable regulation. A flow out of cavity is is only permissible along the shaft portions 3a, 3b and through the openings 28 and 29, since on the amount of leaked fluid, the width of the regulating gap 24 depends. Cover plate 13 is held very closely spaced from stator surface 4a, and when cover plate 13 moves away from surface 4a, the pressure in cavity 15 is immediately increased by fluid flowing out of recess 6, da into the cavity, so that cover plate 13 is again pressed to the right to reduce the thickness of the gap 24 and the amount of fluid discharged into cavity 15.

In the modified arrangement illustrated in FIGS. 3 and 4, two diametrically disposed part-circular grooves 33 and 34 are provided, groove 33 corresponding to groove 22, and groove 34 being symmetrically arranged. Groove 33 is connected by duct 33a to the high pressure side of the pump, while groove 34 is connected by duct 34a to the low pressure side of the pump. Line 36 and the arrows in the upper portion of FIG. 4 indicate the forces acting on cover plate 13. It will be seen that due to the provision of grooves 33 and 34, cover plate 13 can be held in equilibrium so that the tilting moment produced by the pressure in recess 6, 6a is fully compensated. The arrangement illustrated in FIG. 3 has the advantage that a compensation takes place even if the direction of rotation of the machine is reversed. It is also possible to connect one groove with the high pressure side of the machine, and to close the other groove so that an average pressure develops on the closed side.

In order to reduce friction between the rotating cover plate 13 and stator 4, the engaging surface are made as small as possible. As illustrated in MG. 2, the surface 4a is narrower on one side of the pump, and is widened where the groove 22 is provided. Surface portions 41) and 4c are located on opposite sides of groove 22, while a portion of the stator is machined off in the region 4d to make surface in as narrow as possible. In this manner, hydraulic friction losses are reduced.

Hi h pressure oil pumps require very low tolerances in order to achieve a high efficiency, and it is an important advantage of the present invention that no sealing is required at a part of the pump which has a very great diameter, and which is consequently very difficult to cover by a mechanically fitted part. In the arrangement of the present invention, cover plate 13 may be so loosely mounted that it may actually rattle during idle rotation, but when the pumping operation starts, cover plate 13 immediately assumes its proper working position, reducing the gap to the desired thickness, while no nressure is exerted on the rotor.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of rotary piston pumps differing from the types described above.

While the invention has been illustrated and described as embodied in a counterbalanced cover plate for closing the pressure chambers of a rotary piston pump, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

l. A rotary piston pump comprising, in combination, a housing having a cavity and a surface formed with an annular recess communicating with said cavity, said housing having inlet means and outlet means communicating with spaced portions of said recess; a first: rotor mounted in said housing for turning movement about a first axis and having a plurality of pistons projecting in axial direction into said annular recess to transport a fluid from said inlet means to said outlet means; a second lock rotor mounted in said annular recess for free turning movement about a second axis and having circumferentially spaced openings into which some of said pistons project, said lock rotor being rotated by said pistons of said first rotor and fluid-tightly separating said inlet means and said outlet means; and a plate located in said cavity and having at one side a face slidably engaging said surface and covering said annular recess, said plate having circumferentially spaced openings through which said pistons project toward said annular recess and being mounted for rotation about said first aXis so that said plate rotates with said pistons of said first rotor, said plate being mounted also for axial movement so that said face and said surface form a variable gap through which pressure fluid passes from said annular recess into said cavity so that the pressure in said cavity acts on the other side of said plate to urge the same toward said surface to close said annular recess until a condition of equilibrium is reached whereby no axial pressure is exerted on said first rotor.

2. A rotary piston pump comprising, in combination,

a housing having a cavity and a surface formed with an annular recess communicating with said cavity, said housing having inlet means and outlet means communicating with spaced portions of said recess; a first rotor mounted in said housing for turning movement about a first axis and having a plurality of pistons projecting in axial direction into said annular recess to transport a fluid from said inlet means to said outlet means; a second lock rotor mounted in said annular recess for free turning movement about a second axis and having circumferentially spaced openings into which some of said pistons project, said lock rotor being rotated by said pistons of said first rotor and fluid-tightly separating said inlet means and said outlet means; and an annular cover plate located in said cavity and having at one side a face slidably engaging said surface and covering said annular recess, said plate having circumferentially spaced openings through which said pistons project toward said annular recess, said annular plate surrounding said rotor and being mounted for rotation about said first axis so that said plate rotates with said pistons of said first rotor, said plate being mounted also for axial movement so that said face and said surface form a variable gap through which pressure fluid passes from said annular recess into said cavity so that the pressure in said cavity acts on the other side of said plate to urge the same toward said surface to close said annular recess until a condition of equilibrium is reached whereby no axial pressure is exerted on said first rotor.

3. A rotary piston pump comprising, in combination, a housing having a cavity and a surface formed with an annular recess communicating with said cavity, said housing having inlet means and outlet means communicating with spaced portions of said recess; a first rotor mounted in said housing for turning movement about a first axis and having a plurality of pistons projecting in axial direction into said annular recess to transport a fluid from said inlet means to said outlet means; a second lock rotor mounted in said annular recess for free turning movement about a second axis and having circumferentially spaced openings into which some of said pistons project, said lock rotor being rotated by said pistons of said first rotor and fluid-tightly separating said inlet means and said outlet means; a plate located in said cavity and having at one side a face slidably engaging said surface and covering said annular recess, said plate having circumferentially spaced openings through which said pistons project toward said annular recess and being mounted for rotation about said first axis so that said plate rotates with said pistons of said first rotor, said plate being mounted also for axial movement so that said face and said surface form a variable gap through which pressure fluid passes from said annular recess into said cavity so that the pressure in said cavity acts on the other side of said plate to urge the same toward said surface to close said annular recess until a condition of equilibrium is reached whereby no axial pressure is exerted on said first rotor; and means limiting axial movement of said plate away from said surface.

4. A rotary piston pump comprising, in combination, a housing having a cavity and a surface formed with an annular recess communicating with said cavity, said housing having inlet means and outlet means communicating with spaced portions of said recess; a first rotor having shaft means mounted in said housing for turning movement about a first axis and having a plurality of pistons projecting in axial direction into said annular recess to transport a fluid from said inlet means to said outlet means, said shaft means and said housing forming at least one throttling gap connecting said cavity with the outside; a second lock rotor mounted in said annular recess for free turning movement about a second axis and having circumferentially spaced openings into which some of said pistons project, said lock rotor being rotated by said pistons of said first rotor and fluid-tightly separating said inlet means and said outlet means; and a plate located in said cavity and having at one side a face slidably engaging said surface and covering said annular recess, said plate having circumferentially spaced openings through which said pistons project toward said annular recess and being mounted for rotation about said first axis so that said plate rotates with said pistons of said first rotor, said plate being mounted also for axial movement so that said face and said surface form a variable gap through which pressure fluid passes from said annular recess into said cavity and from there through said throttling gap to the outside so that the pressure in said cavity is lower than the pressure in said recess and so that the pressure in said cavity acts on the other side of said plate to urge the same toward said surface to close said annular recess until a condition of equilibrium is reached whereby no axial pressure is exerted on said first rotor.

5. A rotary piston pump comprising, in combination, a housing having a cavity and a surface formed with an annular recess communicating with said cavity, said housing having inlet means and outlet means communicating with spaced portions of said recess, said housing having at least one throttling opening connecting said cavity with the outside; a first roto-r mounted in said housing for turning movement about a first axis and having a plurality of pistons projecting in axial direction into said annular recess to transport a fluid from said inlet means to said outlet means; a second lock rotor mounted in said annular recess for free turning movement about a second axis and having circumferentially spaced openings into which some of said pistons project, said lock rotor being rotated by said pistons of said first rotor and fluidtightly separating said inlet means and said outlet means; and a plate located in said cavity and having at one side a face slidably engaging said surface and covering said annular recess, said plate having circumferentially spaced openings through which said pistons project toward said annular recess and being mounted for rotation about said first axis so that said plate rotates with said pistons of said first rotor, said plate being mounted also for axial movement so that said face and said surface form a variable gap through which pressure fluid passes from said annular recess into said cavity and from there through said throttling opening to the outside so that the pressure in said cavity is lower than the pressure in said recess and so that the pressure in said cavity acts on the other side of said plate to urge the same toward said surface to close said annular recess until a condition of equilibrium is reached whereby no axial pressure is exerted on said first rotor.

6. A rotary piston pump comprising, in combination, a housing having a cavity and a surface formed with an annular recess communicating with said cavity, said housing having inlet means and outlet means communicating with spaced portions of said recess, said surface being formed with a groove in the low pressure region of said inlet means, and said housing having a duct for suppling to said groove fluid from the high pressure region of said outlet means; a first rotor mounted in said housing for turning movement about a first axis and having a plurality of pistons projecting in axial direction into said annular recess to transport a fluid from said inlet means to said outlet means; a second lock rotor mounted in said annular recess for free turning movement about a second axis and having circumferentially spaced openings into which some of said pistons project, said lock rotor being rotated by said pistons of said first rotor and fluidtightly separating said inlet means and said outlet means; and a plate located in said cavity and having at one side face slidably engaging said surface and covering said annular recess, said plate having circumferentially spaced openings through which said pistons project toward said annular recess and being mounted for rotation about said first axis so that said plate rotates with said pistons of said first rotor, said plate being mounted also for axial movement so that said face and said surface form a variable gap through which pressure fluid passes from said annular recess into said cavity so that the pressure in said cavity acts on the other side of said plate to urge the same toward said surface to close said annular recess until a condition of equilibrium is reached whereby no axial pressure is exerted on said first rotor, the pressure of fluid in said groove being added to the pressure prevailing in said gap in the low pressure region of said recess to compensate the higher pressure acting on said face of said plate in the high pressure region of said recess whereby said plate maintains a position in which said face is parallel to said surface.

7. A rotary pump as set forth in claim 6 wherein said surface is formed with another groove in the high pressure region of said outlet means, and wherein said housing has another duct for connecting said other groove with the low pressure region of said inlet means.

8. A rotary piston pump comprising, is combination, a housing having a cavity and a surface formed with an annular recess communicating with said cavity, said housing having inlet means and outlet means communicating with space-d portions of said recess; a first rotor mounted in said housing for turning movement about a first axis and having a plurality of pistons projecting in axial direction into said annular recess to transport a fluid from said inlet means of said outlet means, said first rotor being mounted in said housing for limited axial movement, and having a flange in said cavity carrying said pistons; biasing means for urging said rotor flange toward said surface; a second lock rotor mounted in said annular recess for free turning movement about a second axis and having circumferentially spaced openings into which some of said pistons project, said lock rotor being rotated by said pistons of said first rotor and fluid-tightly separating said inlet means and said outlet means; and a plate located in said cavity and having at one side a face slidably engaging said surface and covering said annular recess, said plate having circumferentially spaced openings through which said pistons project toward said annular recess and being mounted for rotation about said first axis so that said plate rotates with said pistons of said first rotor, said plate being mounted also for axial movement so that said face and said surface form a variable gap through which pressure fluid passes from said annular recess into said cavity so that the pressure in said cavity acts on the other side of said plate to urge the same toward said surface to close said annular recess until a condition of equilibrium is reached whereby no axial pressure is exerted on said first rotor.

9. A rotary piston pump comprising, in combination, a housing having a cavity and a surface formed with an annular recess communicating with said cavity, said housing having inlet means and outlet means communicating with spaced portions of said recess, said housing having at least one throttling opening connecting said cavity with the outside; a first rotor mounted in said housing for turning movement about a first axis and having a plurality of pistons projecting in axial direction into said annual recess to transport a fluid from said inlet means to said outlet means; a second lock rotor mounted in said annual recess for free turning movement about a second axis and having circumferentially spaced openings into which some of said pistons project, said lock rotor being rotated by said pistons of said first rotor and fluid-tightly separating said inlet means and said outlet means; an annular cover plate located in said cavity and having at one side a face slidably engaging said surface and covering said annular recess, said plate having circumferentially spaced openings through which said pistons project toward said annular recess, said annual plate surrounding said rotor and being mounted for rotation about said first axis so that said plate rotates with said pistons of said first rotor, said plate being mounted also for axial movement so that said face and said surface form a variable gap through which pressure fluid passes from said annular recess into said cavity and from there through said throttling opening to the outside so that the pressure in said cavity is lower than the pressure in said recess and so that the pressure in said cavity acts on the other side of said plate to urge the same toward said surface to close said annual recess until a condition of equilibrium is reached whereby no axial pressure is exerted on said first rotor; and means limiting said movement of said plate away from said surface.

it A rotary piston pump comprising, in combination, a housing having a cavity and a surface formed with an annular recess communicating with said cavity, said housing having inlet means and outlet means communicating with spaced portions of said recess, said surface being formed with a groove in the low pressure region of said inlet means, and said housing having a duct for supplying to said groove fluid from the high pressure region of said outlet means said housing having at least one throttling opening connecting said cavity with the outside; a first rotor mounted in said housing for turning movement about a first axis and having a plurality of pistons projecting in flXiZlll direction into said annual recess to transport a fluid from said inlet means to said outlet means; a second lock rotor mounted in said annular recess for free turning movement about a second axis and having circumferentially spaced openings into which some of said pistons project, said lock rotor being rotated by said pistons of said first rotor and fluid-tightly separating said inlet means and said outlet means; and a plate located in said cavity and having at one side a face slidably engaging said surface and covering said annular recess, said plate having circumferentially spaced openings through which said pistons project toward said annular recess and being mounted for rotation about said first axis so that said plate rotates with said pistons of said first rotor, said plate being mounted also for axial movement so that said face and said surface form a variable gap through which pressure fluid passes from said annular recess into said cavity and from there through said throttling opening to the outside so that the pressure in said cavity is lower than the pressure in said recess and so that the pressure in said cavity acts on the other side of said plate to urge the same toward said surface to close said annular recess until a condition of equilibrium is reached whereby no axial pressure is exerted on said first rotor, the pressure of fluid in said groove being added to the pressure prevailing in said gap in the low pressure region of said recess to compensate the higher pressure acting on said face of said plate in the high pressure region of said recess whereby said plate maintains a position in which said face is parallel to said surface.

11. A rotary piston pump comprising, in combination, a housing having a cavity and a surface formed with an annular recess communicating with said cavity, said housing having inlet means and outlet means communicating with spaced portions of said recess, said surface being formed with a groove in the low pressure region of said inlet means, and said housing having a duct for supplying to said groove fluid from the high pressure region of said outlet means said housing having at least one throttling opening connecting said cavity with the outside; a first rotor mounted in said housing for turning movement about a first axis and having a plurality of pistons projecting in axial direction into said annular recess to transport a fluid from said inlet means to said outlet means; a second look rotor mounted in said annular recess for free turning movement about a second axis and having circumferentially spaced openings into which some of said pistons project, said lock rotor being rotated by said pistons of said first rotor and fluid-tightly separating said inlet means and said outlet means; and an an nular cover plate located in said cavity and having at one side a face slidably engaging said surface and covering said annular recess, said plate having circumferentially spaced openings through which said pistons project toward said annular recess, said annular plate surrounding said rotor and being mounted for rotation about said first axis so that said plate rotates with said pistons of said first rotor, said plate being mounted also for axial movement so that said face and said surface form a variable gap through which pressure fluid passes from said annular recess into said cavity and from there through said throttling opening to the outside so that the pressure in said cavity is lower than the pressure in said recess and so that the pressure in said cavity acts on the other side of said plate to urge the same toward said surface to close said annular recess until a condition of equilibrium is reached whereby no axial pressure is exterted on said first rotor; and means limiting axial movement of said plate away from said surface, the pressure of fluid in said groove being added to the pressure prevailing in said gap in the low pressure region of said recess to compensate the higher pressure acting on said face of said plate in the high pressure region of said recess whereby said plate maintains a position in which said face is parallel to said surface.

12. A rotary piston pump comprising, in combination, a housing having a cavity and a surface formed with an annular recess communicating 'with said cavity, said housin g having inlet means and outlet means communicating with spaced portions of said recess, said housing having at tleast one throttle opening connecting said cavity with the outside; a first rotor mounted in said housing for turning movement about a first axis and having a plurality of pistons projecting in axial direction into said annular recess to transport a fluid from said inlet means to said outlet means, said first rotor being mounted in said housing for limited axial movement, and having a flange in said cavity carrying said pistons; biasing means for urging said rotor flange toward said surface; a second look rotor mounted in said annular recess for free turning movement about a second axis and having circumferentially spaced openings into which some of said pistons project, said lock rotor being rotated by said pistons of said first rotor and fluid-tightly separating said inlet means and said outlet means; and an annular cover plate located in said cavity and having at one side a face slidably engaging said surface and covering said annular recess, said plate having circumferentially spaced openings through which said pistons project toward said annular recess, said annular plate surrounding said rotor and being mounted for rotation about said first axis so that said plate rotates with said pistons of said first rotor, said plate being mounted also for axial movement so that said face and said surface form a variable gap through which pressure passes from said annular recess into said cavity and from there through said throttling opening to the outside so that the pressure in said cavity is lower than the pressure in said recess and so that the pressure in said cavity acts on the other side of said plate to urge the same toward said surface to close said annular recess until a condition of equilibrium is reached whereby no axial pressure is exerted on said first rotor.

13. A rotary piston pump comprising, in combination, a housing having a cavity and a surface formed with an annular recess communicating with said cavity, said housing having inlet means and outlet means communicating with spaced portions of said recess, said surface being formed with a groove in the low pressure region of said inlet means, and said housing having a duct for supplying to said groove fluid from the high pressure region of said outlet means, said housing hav ing at least one throttling opening connecting said cavity with the outside; a first rotor mounted in said housing for turning movement about a first axis and having a plurality of pistons projecting in axial direction into said annular recess to transport a fluid from said inlet means to said outlet means, said first rotor being mounted in said housing for limited axial movement, and having a flange in said cavity carrying said pistons; biasing means for urging said rotor flange toward said surface; a second lock rotor mounted in said annular recess for free turning movement about a second axis and having circumferentially spaced openings into which some of said pistons project, said lock rotor being rotated by said pistons of said first rotor and fluid-tightly separating said inlet means and said outlet means; and an annular cover plate located in said cavity and having at one side a face slidably engaging said surface and covering said annular recess, said plate having circumferentially spaced openings through which said pistons project toward said annular recess, said annular plate surrounding said rotor and being mounted for rotation about said first axis so that said plate rotates with said pistons of said first rotor, said plate being mounted also for axial movement so that said face and said surface form a variable gap through which pressure passes from said annular recess into said cavity and from there through said throttling opening to the outside so that the pressure in said cavity is lower than the pressure in said recess and so that the pressure in said cavity acts on the other side of said plate to urge the same toward said surface to close said annular recess until a condition of equilibrium is reached whereby no axial pressure is exerted on said first rotor, the pressure of fluid in said groove being added to the pressure prevailing in said gap in the low pressure region of said recess to compensate the higher pressure acting on said face of said plate in the high pressure region of said recess whereby said plate maintains a position in Which said face is parallel to said surface.

14. A rotary piston pump comprising, in combination, a housing having a stator portion and a cavity adjacent one surface of said stator portion, said stator portion being formed in said surface with an annular recess having two eccentric partly coinciding circular recess portions, said housing having inlet means and outlet means connected with said recess; a first rotor mounted in said housing for turning movement about a first axis and having a plurality of pistons projecting in axial direction into one of said circular recess portions of said annular recess to transport a fluid from said inlet means to said outlet means; a second look rotor mounted in the other of said circular portions of said annular recess for free turning movement about a second axis and having circumferentially spaced openings into which some of said pistons project in the region where said recess portions coincide, said lock rotor being rotated by said pistons of said first rotor and fluid-tightly separating said inlet means and said outlet means in said region; and a plate located in said cavity and having at one side a face slidably engaging said surface and covering said annular recess, said plate having circumferentially spaced openings through which said pistons project toward said annular recess and being mounted for rotation about said first axis so that said plate rotates with said pistons of said first rotor, said plate being mounted also for axial movement so that said face and said surface form a variable gap through which pressure fluid passes from said annular recess into said cavity so that the pressure in said cavity acts on the other side of said plate to urge the same toward said surface to close said annular recess until a condition of equilibrium is reached whereby no axial pressure is exerted on said first rotor.

15. A rotary piston pump comprising, in combination, a housing having a stator portion and a cavity adjacent one surface of said stator portion, said stator portion being formed in said surface with an annular recess having two eccentric partly coinciding circular recess portions, said housing having inlet means and outlet means connected with said recess, said housing having at least one throttling opening connecting said cavity with the outside; a first rotor mounted in said housing for turning movement about a first axis and having a plurality of pistons projecting in axial direction into one of said circular recess portions of said annular recess to transport a fluid from said inlet means to said outlet means; a second lock rotor mounted in the other of said circular portions of said annular recess for free turning movement about a second axis and having circumferentially spaced openings into which some of said pistons project in the region where said recess portions coincide, said lock rotor being rotated by said pistons of said first rotor and fluid-tightly separating said inlet means and said outlet means in said region; and an annular cover plate located in said cavity and having at one side a face slidably engaging said surface and covering said annular recess, said plate having circumferentially spaced openings through which said pistons project toward said annular recess, said annular plate surrounding said rotor and being mounted for rotation about said first axis so that said plate rotates with said pistons of said first rotor, said plate being mounted also for axial movement so that said face and said surface form a variable gap through which pressure fluid passes from said annular recess into said cavity and from there through said throttling opening to the outside so that the pressure in said cavity is lower than the pressure in said recess and so that the pressure in said cavity acts on the other side of said plate to urge the same toward said surface to close said annular recess until a condition of equilibrium is reached whereby no axial pressure is exerted on said first rotor.

16. A pump as set forth in claim 15 wherein said first rotor has shaft portions of different diameter; and wherein said housing includes bearings for said shaft portions, said cavity communicating with said bearings so that fluid leaks through the same.

17. A pump as set forth in claim 16 wherein one of said bearings has a greater diameter and is provided in said stator portion.

18. A rotary piston pump, comprising a housing defining a cavity and having a surface provided with an annular recess communicating with said cavity, said housing further having inlet means and outlet means communicating with spaced portions of said recess; a first rotor mounted in said housing for rotation about a first axis and having a plurality of pistons extending in the axial direction of said rotor and into said recess to transport a 4 fluid from said inlet means to said outlet means; a lock rotor mounted in said recess and rotatable about a second axis, said lock rotor having a plurality of circumferentially spaced openings into which some of said pistons project, said lock rotor being rotated by said pistons and fluid-tightly separating said inlet means from said outlet means; a plate located in said cavity and having at one side a face slidably engaging the surface of said housing and overlying said recess, said plate having circumferentially spaced openings through which said pistons project into said recess and being mounted for rotation with said pistons about said first axis, said plate being movable axially of said rotor so that said face and said surface may form a variable gap through which pressure fluid passes from said recess into said cavity whereby the pressure prevailing in said cavity acts on the other side of said plate to urge the same toward said surface and to reduce the width of said gap until a condition of equilibrium is reached in which condition no axial pressure is exerted on said first rotor; and resilient means for biasing said plate against said surface.

19. A rotary piston pump as set forth in claim 18, wherein said resilient means comprises helical springs extending into recesses provided in said first rotor and bear ing against the other side of said plate.

References Cited by the Examiner UNITED STATES PATENTS Re. 25,801 6/1965 Noren 103126 1,196,315 8/1916 Vincent 9168 1,994,397 3/1935 Loveridge et al 9168 2,998,783 9/1961 Lee 103-126 3,038,413 6/1962 Erneny et a1. 103-426 3,224,198 12/1965 Schimkat 103--126 FOREIGN PATENTS 977,510 11/ 1950 France. 873,208 4/ 1953 Germany.

MARK NEWMAN, Primary Examiner.

W. J. GOODLIN, Assistant Examiner. 

1. A ROTARY PISTON PUMP COMPRISING, IN COMBINATION A HOUSING HAVING A CAVITY AND A SURFACE FORMED WITH AN ANNULAR RECESS COMMUNICATING WITH SAID CAVITY, SAID HOUSING HAVING INLET MEANS AND OUTLET MEANS COMMUNICATING WITH SPACED PORTIONS OF SAID RECESS; A FIRST ROTOR MOUNTED IN SAID HOUSING FOR TURNING MOVEMENT ABOUT A FIRST AXIS AND HAVING A PLURALITY OF PISTONS PROJECTING IN AXIAL DIRECTION INTO SAID ANNULAR RECESS TO TRANSPORT A FLUID FROM SAID INLET MEANS TO SAID OUTLET MEANS; A SECOND LOCK ROTOR MOUNTED IN SAID ANNUALR RECESS FOR FREE TURNING MOVEMENT ABOUT A SECOND AXIS AND HAVING CIRCUMFERENTIALLY SPACED OPENINGS INTO WHICH SOME OF SAID PISTONS PROJECT, SAID LOCK ROTOR BEING ROTATED BY SAID PISTONS OF SAID FIRST ROTOR AND FLUID-TIGHTLY SEPARATING SAID INLET MEANS AND SAID OUTLET MEANS; AND A PLATE LOCATED IN SAID CAVITY AND HAVING AT ONE SIDE A FACE SLIDABLY ENGAGING SAID SURFACE AND COVERING SAID ANNULAR RECESS, SAID PLATE HAVING CIRCUMFERENTIALLY SPACED OPENINGS THROUGH WHICH SAID PISTONS PROJECT TOWARD SAID ANNULAR RECESS AND BEING MOUNTED FOR ROTATION ABOUT SAID FIRST AXIS SO THAT SAID PLATE ROTATES WITH SAID PISTONS OF SAID FIRST ROTOR, SAID PLATE BEING MOUNTED ALSO FOR AXIAL MOVEMENT SO THAT SAID FACE AND SAID SURFACE FORM A VARIABLE GAP THROUGH WHICH PRESSURE FLUID PASSES FROM SAID ANNULAR RECESS INTO A SAID CAVITY SO THAT THE PRESSURE IN SAID CAVITY ACTS ON THE OTHER SIDE OF SAID PLATE TO URGE THE SAME TOWARD SAID SURFACE TO CLOSE SAID ANNULAR RECESS UNTIL A CONDITION OF EQUILIBRIUM IS REACHED WHEREBY NO AXIAL PRESSURE IS EXERTED ON SAID FIRST ROTOR. 